A total organic carbon measurement apparatus uses either a combustion oxidation method of burning and oxidizing organic matter in a hot furnace, or a wet oxidation method of oxidizing organic matter in an organic matter oxidative decomposition unit using an ultraviolet light. The latter wet oxidation method is generally used for high-sensitive measurement of pure water or ultrapure water. The present invention is also directed to a total organic carbon measurement apparatus using the latter wet oxidation method.
As a method for measuring total organic carbon by a wet oxidation method, a known method involves providing, downstream of an organic matter oxidative decomposition unit, a carbon dioxide separation unit using a gas permeable membrane through which carbon dioxide passes, moving carbon dioxide in sample water into measurement water composed of deionized water, and measuring conductivity of the measurement water (see Patent Literature 1).
Further, there is proposed a total organic carbon measurement apparatus that uses a micromachining technique to integrate a device, thereby reducing consumption of samples or reagents and reducing elution or permeation from a pipe (see Patent Literatures 2 and 3). The total organic carbon measurement apparatus includes an organic matter oxidative decomposition unit that oxidizes organic matter in supplied sample water into carbon dioxide by ultraviolet irradiation, a carbon dioxide separation unit that moves the carbon dioxide in the sample water, which has gone through the organic matter oxidative decomposition unit, into measurement water composed of deionized water through a gas permeable membrane, and a detection unit that measures conductivity of the measurement water having gone through the carbon dioxide separation unit to obtain a carbon dioxide concentration, and at least in the carbon dioxide separation unit among the units, the sample water flows through a minute flow line formed in a chip.
In order to move the carbon dioxide in the sample water through the gas permeable membrane to the measurement water, the sample water is kept acidic so that the carbon dioxide in the sample water is gaseous. For this purpose, generally, inorganic acid containing no carbon component is added to the sample water to keep the sample water highly acidic, for example, at pH of about 2. As such acid, phosphoric acid or sulfuric acid is used.
Inorganic carbon (IC) originally dissolved in the sample water is also removed to measure a TOC concentration. For this purpose, acid is added to the sample water to be supplied to the organic matter oxidative decomposition unit, and an inorganic carbon component is removed by aeration with a carrier gas containing no carbon component, and then the sample water is supplied to the organic matter oxidative decomposition unit.